A passive RFID sensor tag antenna transducer

Passive radio frequency identification (RFID) sensor transponders (tags) are realized by integrating a passive transducer structure that changes its impedance with its environment. The change in impedance directly modulates the backscattered signals in amplitude and phase. Consequently, an RFID reader can wirelessly detect changes in the tag environment. This paper presents an antenna transducer that maps its sensor information to the phase of the backscatter signal in the absorbing mode. The main advantage of this transducer is that it benefits a constant amplitude of the backscatter signal in the absorbing mode and thus provides a reliable power transfer to the passive tag.